创建新的/下一个Android活动时遇到的问题

Question

I just wanted to click on a button in the MainActivity. After I clicked on this button a new activity appears. In this activity is also a button and when I click on this button a text appears. My Problem now is, that the text doesn't appear, when I click on the button. My code for clicking on a button so that a text appears is actually working. But not if I use it in a new Activity/Layout/ page. So there must be s.th. wrong with the Connection between the first and the second activity?!

MainActivity.java:

package com.example.xxx;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;}
        {}
    public void page2 (View view){
        setContentView(R.layout.pagetwo);


}}

activity_main.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/BtnKlick"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:layout_marginTop="178dp"
        android:text="Button" 
        android:onClick="page2"/>

</RelativeLayout>

Pagetwo.java:

package com.example.xxx;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class Pagetwo extends Activity implements OnClickListener {

    public Button btn1;
    public TextView tw1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.pagetwo);

    btn1 = (Button) findViewById(R.id.BtnKlick);
    tw1 = (TextView) findViewById(R.id.Text);

    btn1.setOnClickListener(this);

}
    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub

        tw1.setText("Hallo");

    }}

pagetwo.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <Button
        android:id="@+id/BtnKlick"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="Klick" />

    <TextView
        android:id="@+id/Text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="87dp" />

</RelativeLayout>

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.xxx"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.xxx.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Answer 1

Update

All you seem to be doing is swapping your layouts within PageOne activity.

Change

public void page2 (View view){
    setContentView(R.layout.pagetwo);
}

to

public void page2 (View view){
Intent i = new Intent(this, Pagetwo.class);             
    startActivity(i);
}

This will actually launch your pagetwo activity rather than just swapping layouts within pageone activity

Make that change and all should be good. You will most likely have to add some imports, at least for the intent class

Also Activities must be registered in the manifest. To add the activity to your manifest check the code below

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="com.example.xxx.MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <activity
        android:name="Pagetwo"
        android:label="@string/app_name" >
    </activity>

</application>

Change the label to something more appropriate than app name once you have it working End update

Try renaming your xml view id's to meet coding standards by using all lower case letters and separating words with underscores. The Android platform may well be getting confused as Text is a reserved word.

so

<TextView
    android:id="@+id/Text"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="71dp"
    android:textSize="70sp" />

becomes

<TextView
    android:id="@+id/tv_hallo"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="71dp"
    android:textSize="70sp" />

and your code becomes

...
    public TextView tw;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.eclipse);

        btn = (Button) findViewById(R.id.BtnKlick);
        tw = (TextView) findViewById(R.id.tv_hallo);

        btn.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub

        tw.setText("Hallo");

    }
...

Not sure if this is going to have much of an effect but it is just possible android is getting the word Text confused

Also check your logcat output to see if there are any errors.